Establishment And Evaluation Of Graded Neuropathic Pain Developed By Graded Sciatic Constriction In Mouse Model

To develop a mouse model of graded neuropathic pain by graded sciatic constriction and to assess the behavioral,ultrastructure changes of sciatic nerve,spinal microglia activation,and expressions of cytokines in the spinal cord of the model.And to observe the effect of electro-acupuncture on painful behavior and expression of IL-1? ?IL-6?TNF-? in the spinal cord with graded sciatic constriction in mouse model.Methods: 32 male C57/BL6 mice were randomly allocated equally in 4 groups(group N0?N1?N2 and N4,n=8 for each group)and received graded right sciatic constriction.Paw withdrawal threshold and thermal withdraw latency was measured before operation and on the 1st to 29 th postoperative days.On the 14 th and 29 th postoperative days,the right sciatic nerve and the lumbar cord were obtained to analyze ultrastructure changes of the sciatic nerve by transmission electron microscope and to compute the percentage of abnormal myelin sheath.The immunohistochemisty was employed to evaluate the spinal microglia activation by the integral optical density(IOD)of OX-42.The spinal levels of IL-1?,IL-6 and TNF-? was measured by enzyme-linked immunosorbent assay(ELISA).And 56 male C57/BL6 mice were randomly allocated equally in group N0?N1?N1+E?N2?N2+E?N4?N4+E(n=8)and received graded right sciatic constriction.EA was applied for N1+E ? N2+E ? N4+E to bilateral ”Huantiao” and ”Zusanli” acupointsand eletro-acupuncture.The paw withdrawal threshold was measured before operation and at the 2d?4d?6d?8d?10d?12d?14d postoperative days.On the 14 th postoperative days,the lumbar cord were obtained to determine the expressions of IL-1?,IL-6 and TNF-? via enzyme-linked immunosorbent assay(ELISA).Results: The paw withdrawal threshold and thermal threshold of the right foot dropped dramatically in group N1?N2 and N4 compared with N0(P<0.05).On the 14 th and 29 th postoperative days,outcomes of the ultrastructure showed that in group N0,majority of the nerve fibers were normal,and in group N1?N2 and N4,extensive onion-like state of the myelin sheath of the right sciatic nerve fibers,shrink or disappearance of axon,kytoplasm edema or lysis of Schwann cells tending to necrosis.Compared with group N0,the percentage of abnormal myelin sheath,IOD of OX-42 and the IL-1? ?IL-6?TNF-? were increased differently in group N1?N2 and N4(P<0.05).Compared with N1,the paw withdrawal threshold of the right foot significantly increased after EA therapy in group N1+E(P<0.05),but no significant difference in group N2+E and N4+E.The expressions of IL-1? ?IL-6?TNF-? in group N1?N2 and N4 were higher than that of group N0(P<0.05).EA can decrease the expression of IL-1? ?IL-6?TNF-? in group N1+E and IL-1? in group N2+E(P<0.05),but no significant difference in group N4+E.Conclusion: The graded model of neuropathic pain can be developed by graded constriction of the sciatic nerve,and lead to different degrees of demyelnation,spinal microglia activation and increase the expression of the IL-1? ?IL-6 and TNF-?.EA may reduce hyperalgesia caused by graded sciatic constriction in mouse model and decrease the expression of IL-1? ?IL-6 and TNF-? in the spinal cord.